This application claims priority to German patent application no. 10044378.8, filed Sep. 7, 2000.
The invention concerns a roller cage for guiding a minimum of one work roller of a tool for deep rolling of radii or grooves of crankshaft journals or crank pins, where the roller cage is supported at the end of the long leg of an L-shaped tool holder, and loosely guided in the longitudinal direction of the long leg by means of a tab which engages in a longitudinal groove on the underside of the roller cage from the end of the long leg.
A deep rolling tool is described in European Patent Application EP 0 839 607 A1. This known tool is designed for deep rolling of radii or grooves of crankshaft journals or crank pins. Deep rolling is implemented using deep rolling work rollers which are pressed with a specific force into the radii or grooves of crankshaft bearings while the crankshaft rotates. The work rollers are guided in so-called roller cages of prismatic shape and supported at the end of the long leg of an L-shaped tool holder. The guidance is of a floating nature and has a tab projecting from the end of the long leg that engages in a groove on the underside of the roller cage. The floating connection is configured in a way to provide the roller cage, and thereby the work roller, with a limited movement in the axial direction, i.e., in the longitudinal direction of the long leg of the L-shaped tool holder.
Crankshafts will, however, have processing tolerances. These may be of the kind where the spacing between radii or grooves of one and the same bearing differs from that of other bearings. Also, a crankshaft may have differences in length with respect to the location of bearings in the crankshaft axial direction.
Generally, bearings of a crankshaft used in engines of motor vehicles, are deep rolled on a deep rolling machine simultaneously in one operation. To this end a plurality of deep rolling tools are arranged in the deep rolling machine side by side having lateral distances equal to the distances of the crankshaft bearings. Due to process related variations in length between the individual bearings, which may have a magnitude of a few millimeters, the fixed configuration of deep rolling tools within the deep rolling machine causes some deep rolling tools to be subjected to more stress than others. This in turn leads to variations in the wear and tear of deep rolling tools. Deep rolling tools are items of high precision which to a certain degree are capable of adjusting to the manufacturing tolerances of the work. For this reason, higher manufacturing tolerances of crankshafts may reduce the tool life requiring a more frequent change of individual, or all, tools of a deep rolling machine.
The object of the following invention calls for the configuration of a deep rolling tool that enables it to compensate for longitudinal tolerances at the bearings of crankshafts. The respective deep rolling tool must be configured to allow unrestricted compliance with the specified precision during the deep rolling of a crankshaft bearing. In addition the deep rolling tool must be reliable, easy to handle and reasonably priced.
Surprisingly it was found that for compensation of process related tolerances in the longitudinal direction of a crankshaft, it suffices to design a minimum of one of the two roller cages of a deep rolling tool in which the work rollers are guided, with floating capability perpendicular to the working direction. The simplest approach found for this is to provide the longitudinal groove of the roller cage with a substantially greater width than the tab retaining the roller cage to the deep rolling tool. A difference in width between 0.5 and 2.5 mm has shown to be sufficiently large.
It is however even more advantageous to suspend the roller cage at the tool holder in a self-centering fashion, perpendicular to its working direction. To this end, a minimum of one additional element is provided at the end of the long leg of the tool holder, which engages in a recess provided on the face of the roller cage facing the end of the long leg of the tool holder. This element was found to be especially simple when configured as a round pin that is also spherical at its front end with which it engages the respective recess of the roller cage.
A recess in the roller cage, configured in a rather simple manner is obtained by means of a blind hole whose diameter is substantially greater than the diameter of the round pin, and which at its bottom has the shape of a cone. When the pin is supported elastically at the end of the L-shaped leg of the tool holder, the pin centers itself automatically at the cone shaped bottom of the hole representing the recess in the roller cage. This self-centering feature can be even more effective if the pin in the long leg of the L-shaped tool holder is also supported elastically in the axial direction.
For the simplest application one single pin will suffice which engages the roller cage from the end of the long leg of the L-shaped tool holder. It is however more advantageous to allocate one dedicated pin to each work roller guided by the roller cage. Generally, one roller cage serves to guide two work rollers.
Each of the recesses engaged by the ends of the pins, has a greater diameter than the pins themselves in order to assure sufficient flexibility of the roller cage perpendicular to its working direction. As with the differences in width between groove and tab, the diametrical differences have a magnitude between 0.5 and 2.5 mm.